Myopic patients can now undergo radial keratotomy procedures in order to achieve refractive correction. During these keratorefractive procedures, surgeons reconfigure the myopic patient's cornea so that the light entering the eye focuses more accurately on the retina. Surgical knives which make precise radial incisions in the cornea assist the surgeons in performing this reconfiguration.
The goal of both the surgeon and the patient during a radial keratotomy procedure is to achieve refractive correction. This goal has not always been reached, however, because of the many potential problems which a surgeon may encounter. One danger of the procedure involves an undesired invasion of the central optical zone, caused by slight irregular movements of the patient's eye or the surgeon's hand. Incisions invading the superficial layers of the optical zone are associated with optical glare, since the resulting surface scarring has a different refractive index than the surrounding corneal tissue. Another potential problem involves the risk of puncturing the cornea during the incision process. Such a puncture could create an entrance for bacteria to enter the anterior chamber of the eye, with the attendant risks of infection and complications.
In order to minimize the above described problems, surgical knives have been designed with special features. One such special feature is the foot portion, one or more feet attached to the blade holder which frame the distal end of the blade. The foot portion helps surgeons monitor the incision making process by controlling incision depth. The foot portion acts as a limit to incision depth, since the knife blade must stop penetrating the corneal tissue when the foot portion comes in contact with such tissue. In this way, the foot portion assists the surgeon in controlling the depth of the incisions.
Modern foot plates for radial keratotomy knives have been known to assume an "American," "Russian," or "Universal" configuration. The American foot plate generally has a small contact surface at its distal end and an oblique angled surface for permitting the oblique cutting edge of an American-style diamond knife to reveal its cutting edge. The Russian foot portion is designed with a larger surface for contacting the cornea and exhibits a right-angle configuration. Since Russian cutting edges are substantially vertical, the Russian feet do not exhibit an oblique surface. More recently, a Universal foot portion which exhibits properties of the American and Russian feet has been developed for combined incision blades. The Universal foot portion is more open than an American foot portion for permitting greater visibility of the blade, but it retains a small contact surface.
Although the purpose of the foot portion is to aid surgeons in controlling the precise nature of the incisions, some of the designs of the currently available foot portions have hindered this requisite precision. Many foot portions of currently available surgical knives are attached to the knife body in a fixed position. The blade and foot plate of these knives move over the corneal tissue together as the blade is used to make the incision. Although the foot plate is designed to slide over the tissue, this movement is not always smooth, and provides a source of friction, which can disrupt the motion of the knife blade penetrating the corneal tissue. This inability of the knife blade to move independently of the foot portion has thus hindered the success rate of keratorefractive surgery, since any disruption of free movement which is experienced by the foot portion will necessarily affect the incision.
The contact between the fixed foot plate and the corneal tissue can also lead to a tissue bulge in the area around foot plate contact. When the fixed foot plate exerts pressure on the portion of the corneal tissue over which it slides, the surrounding tissue responds to this pressure by bulging upward, away from the plane of the incision. This tissue bulging is disadvantageous to surgeons, as it interferes with the precision required for the radial incisions.
Accordingly, there is a present need for foot portions that move independently from the knife blade and do not cause tissue bulging. There is also a need to permit greater visibility of the knife blade during surgery while still allowing the blade to move freely through the cornea during incisions. Such a foot portion, to be effective, must still act as a limit to incision depth and length.